Detonator



Fgb. 19, 1935. A] Ew 1,991,857

DETONATOR Filed May 2, 1953 .Yfaroldfilewlb' INVENTOR.

ATTORNE Y.

Patented Feb. 19, 1935 UNITED STATES e DETONATOR Harold A. Lewis,Woodbnry, N. J assignor to E. I.

du' Pont de Nemours & Company, Del., a corporation of Delaware PATENTOFFICE Wilmington,

Application May 2, 1933, Serial No. 668,921

3 Claims.

This invention relates to an improved detonator and more particularly toa detonator adapted for use as a fuse connector for connecting one lineof detonating fuse to another-line, in order that detonation of thesecond line from the first may be assured.

Several kinds of detonating fuses are known, of which Cordeau is the onemost commonly used. This consists of a small lead tube filled with anexplosive compound, trinitrotoluene for example, which has a very highvelocity of detonation, over 16,000 feet per second at the densityemployed. Cordeau is used principally in deep welldrill holes and inother large blasts where it is desired that a number of differentcharges shall explode almost simultaneously. The extreme violence withwhich it explodes is suflicient to detonate high explosives adjacentto-it in a bore hole so that Cordeau finds particular use in thismanner. In actual work in the field, Cordeau is brought to explosion bymeans of ordinary or electric blasting caps, which must be in directcontact with the explosive compound contained in the Cordeau.

In the use of Cordeau and in connecting the main line of fuse with thebranch lines leading to the separate bore holes, various methods havebeen used. The usual practice, however, has been to split a section ofthe branch line of Cordeau for the distance of about 3" at the end, andto pullthe split ends apart to form a crotch. The main or trunk line ofCordeau is placed well down in these crotches, and the split ends arewrapped around themain line, one to the right and the otherto the left.A blasting cap connected to the end of the line of fuse is fired in'order to bring about the detonation of the entire blast.

Another type of fuse, which has been employed, consists of .a highexplosive core contained in a flexible and combustible outer covering.One form used, for example, has contained pentaerythrite tetranitrate asthe high explosive, covered with collodion and"counterings of cottoncord, rubber and the like, either by themselves or in combination. Theadvantage of such fuse lies in the higher velocity of detonation,approximately 22,000 feet per second. An additional point of superiorityhas been claimed, namely that, with such detonating fuse, branch linesmay be satisfactorily connected by simply tying to the main line.

The practice outlined in the foregoing has the disadvantage. thatmisfires frequently occur, in the case of Cordeau, at the connection ofthe trunk line with the branch lines extending into the bore holebecause of the poor contact of the material in the two lines of fuse. Afurther and importantdisadvantage comes from the fact that such aconnection is not water-tight. Another drawback is that, while thedetonation wave is usually propagated to branch lines leading ofi atangles not greater than 90, the propagation is questionable when thebranch line goes off at an obtuse angle.

A more satisfactory method of making a connection between the ain lineof detonating fuse andthe branch lin s consists in employing a modifiedform of. lasting cap shell adapted to fit over the end ofthe branch lineof fuse, and having its closed end secured to means adapted to engagethe main line. In fitting such a shell onto the fuse, the cap can becrimped tightly. Using such a method the advantages obtained are that awater-tight connection is secured, that the likelihood is reduced of theoccurrence of misfires, and that propagation is certain even when thecommunicating fuse line leads off at an obtuse angle.

The object of my invention is to provide a detonator suitable for thelatter method of connecting fuse lines. A further object is adetonator'having its primary and secondary charges so arranged as tointroduce the minimum of hazard and to bring about the propagation ofthe detonation'most certainly from one line of detonating fuse to theother. A still further object is a detonator containing a minimumprimary charge and attaining its maximum velocity almostinstantaneously. Additional objects will be disclosed as the inventionis described further.

These objects are accomplished according to my invention, wherein adetonator is provided consisting of a tubular shell containing a primarycharge of lead azide and a secondary or main charge of a' detonatingexplosive. Contrary to the usual practice in the loading of blastingcaps, however, my invention places the primary charge of lead azide atthe bottom of the cap adjacent to the closed end of the shell. Thesecondary charge is then loaded on the top of the lead azide. Preferablythe cap shell has arrangements also for the ready attachment of itsclosed end to the main line of fuse.

In order to illustrate more clearly my invention, reference is made tothe accompanying drawing, in Figure I of which 1 represents a tubularshell, preferably of aluminum, 2 a secondary charge of explosive such astetryl, and 3 a primary of lead azide. a designates a cap to the mainline of Cordeau, though such bead is not a part of my invention. When inuse in the field as a fuse connector, the cap shell will fit over theend of the branch line of detonating fuse leading to the bore hole thefuse being inserted until it rests against the charge 2. ,The detonatoris then crimped firmly onto the fuse.

The detonator is brought to the main line of fuse and fastened so thatthe closed end is butted up against the trunk line and secured in thatposition.

Figure 2 illustrates one method of use of such a detonator as adetonating fuse connector, in which the shell 6 encloses the end of thefuse line '7. The bead at the upper end of the shell engages a clip 8 byinsertion of the detonator 6 through an opening in the base of the clipuntil the edges of the opening engages the bead. The clip can thenreadily be made secure to the main line of detonating fuse 5.

I find lead azide the most suitable primary charge for my detonator.Lead azide, has the combined advantages over all other primarydetonating compounds of safety in use and immediate pick-up to itsmaximum velocity. Because of this latter property, this compound, for agiven weight of material, attains its maximum velocity quicker thanother primary detonating compounds such as mercury fulminate. Myinvention is directed, therefore, to the use of lead azide as a primarycharge. As a secondary charge I may use various suitable high explosivecompounds, taken preferably from the three classes that may bedesignated as -(1) nitramines, (2) solid nitric esters, and (3) aromaticnitrocompounds. As suitable secondary charges from the foregoingclasses, I may cite trimethylene trinitramine and tetryl in class 1,pentaerythrite tetranitrate, erythritol tetranitrate, and nitrostarch inclass 2, and trinitrotoluene and picric acid in class 3. Preferably Iemploy tetryl. .In

loading my improved detonator, the lead azide is first presssd to thebottom of the shelLfor example, 3.5 grains. On top of this is pressedthe desired amount of the secondary charge.

Whereas the customary way of loading detonators is to introduce thesecondary charge first and to superimpose the primary charge on thischarge, which is the logical arrangement for the usual method ofemploying such detonators, my detonator, with .the positions of theprimary and secondary charges reversed, possesses great advantages undercertain conditions of use. For example, when the detonator is employedin the manner suggested heretofore, namely for connecting branch linesto main lines of .detonating fuse, such a reversed arrangement ofcharges has the particular advantage of making .the detonator much saferin handling and use, since the relatively insensitive secondary chargeis the one that is exposed to the friction of the end of the branchline. In this way all hazards of premature detonation from this causeare removed.

It will be understood that my invention is not limited to any particulartype of shell. While aluminum is my preferred shell metal, any metalcompatible with lead azide may be employed. Similarly, my improveddetonator may be applied to uses other than as a fuse connector, in factin all places where thearrangement described gives advantages. It willbe understood also, of course, that the bead or other arrangement on theshell for facilitating the attachment of the detonator. to a fuse lineis not a part of my invention. I intend to be limited in my inventiononly as indicated in the following patent claims.

I claim:

1. A detonator or blasting cap comprising a shell or tube having aclosed end, a'secondary or main charge, and a primary charge ofdetonating material in the tube, the primary charge being nearest to theclosed end of the tube.

2. The detonator or blasting cap of claim 1 in which the primary chargecomprises fulminate of mercury.

3. The detonator or blasting cap of claim 1 in which the main chargecomprises tetryl.

HAROLD A. LEWIS.

